Polymer ultrapermeability from the inefficient packing of 2D chains

The promise of ultrapermeable polymers, such as poly(trimethylsilylpropyne) (PTMSP), for reducing the size and increasing the efficiency of membranes for gas separations remains unfulfilled due to their poor selectivity. We report an ultrapermeable polymer of intrinsic microporosity (PIM-TMN-Trip) that is substantially more selective than PTMSP. From molecular simulations and experimental measurement we find that the inefficient packing of the two-dimensional (2D) chains of PIM-TMN-Trip generates a high concentration of both small (<0.7 nm) and large (0.7–1.0 nm) micropores, the former enhancing selectivity and the latter permeability. Gas permeability data for PIM-TMN-Trip surpass the 2008 Robeson upper bounds for O2/N2, H2/N2, CO2/N2, H2/CH4 and CO2/CH4, with the potential for biogas purification and carbon capture demonstrated for relevant gas mixtures. Comparisons between PIM-TMN-Trip and structurally similar polymers with three-dimensional (3D) contorted chains confirm that its additional intrinsic microporosity is generated from the awkward packing of its 2D polymer chains in a 3D amorphous solid. This strategy of shape-directed packing of chains of microporous polymers may be applied to other rigid polymers for gas separations

Quantum Energy-Transport and Drift-Diffusion Models

We show that Quantum Energy-Transport and Quantum Drift-Diffusion models can be derived through diffusion limits of a collisional Wigner equation. The collision operator relaxes to an equilibrium defined through the entropy minimization principle. Both models are shown to be entropic and exhibit fluxes which are related with the state variables through spatially non-local relations. Thanks to an � expansion of these models, � 2 perturbations of the Classical Energy-Transport and Drift-Diffusion models are found. In the Drift-Diffusion case, the quantum correction is the Bohm potential and the model is still entropic. In the Energy-Transport case however, the quantum correction is a rather complex expression and the model cannot be proven entropic.

Ultrasensitive broadband infrared 4x4 Mueller matrix ellipsometry for studies of depolarizing and anisotropic thin films

The authors present a second generation broadband 4 x 4 Mueller matrix MM ellipsometer for ultrasensitive infrared spectroscopic 8000 800 cm 1 studies of complex nanometer thin films. In a modular design, the instrument employs retractable achromatic retarders and various sets of tandem polarizers. Using high transmittance free standing wire grid polarizers, the device reaches an unparalleled precision of up to 5 x 10 5 in the important fingerprint region, even for block offdiagonal MM elements. Broadband and signal to noise optimized access to the full 4x 4 MM provides in depth information on the sample s polarimetric properties and opens the door for detailed explorations of depolarizing and anisotropic materials. The authors discuss examples of highly depolarizing nonuniform polyimide membranes, uniaxial to biaxial anisotropy changes in ultrathin polymer films, and azimuthal off axis effects in 2D structured silica arrays. Diverse optical modeling approaches based upon anisotropic layer stacks and rigorous coupled wave analysis are used to quantify the optical, structural, and chemical properties of the sampl

An efficient method for preparing high molecular weight polymers of intrinsic microporosity (PIM)s with cyclic-free structure via fast polycondensation

Peer reviewed: YesNRC publication: Ye

Gas transport behavior of membranes composed of silica nanoparticles in polymers of intrinsic microporosity (PIM)

Peer reviewed: YesNRC publication: Ye

Olefin Recovery from Chemical Industry Waste Streams

The objective of this project was to develop a membrane process to separate olefins from paraffins in waste gas streams as an alternative to flaring or distillation. Flaring these streams wastes their chemical feedstock value; distillation is energy and capital cost intensive, particularly for small waste streams